CES造有開口耐震壁のせん断伝達機構に及ぼす上下層開口位置の影響

Abstract

The shear strength of multistory shear walls with openings is affected by the opening arrangement in each story because the shear transferring mechanism changes depending on the location of openings in the upper and lower stories. In this study, static loading test and Three-dimensional (3D) FEM analysis for multistory concrete encased steel (CES) shear walls with openings were conducted to investigate the effect of the opening arrangement in two continuous stories on the shear transferring mechanism. Outlines and results of the test and analysis are described in this paper. The validity of the modified strut model proposed by the authors to estimate the shear strength of CES shear walls with openings is also examined using the experimental and analytical results. Three CES shear walls of two stories which were about one-third scale were tested. The variable investigated was the opening arrangement. Specimen CWO2 had an opening arranged in the center of wall panel in each story, Specimen CWO3 had an opening eccentrically arranged in the one side of the wall panel in each story, and Specimen CWO4 had an opening in each story which is diagonally arranged between the upper and lower stories. The compressive failure of wall panel around an opening in each story occurred in Specimen CWO2. On the other hand, the shear failures of wall panel in the first story occurred in Specimens CWO3 and CWO4. The maximum strength of Specimen CWO4 with diagonally arranged openings was higher than that of Specimen CWO3 with eccentrically arranged openings, when the boundary column adjacent to the opening in the first story was subjected to tension. The shear strengths of CES shear walls with openings calculated by the modified strut model almost agree with the test results. Since the modified strut model cannot take into account the difference of opening location in the upper story, calculated results between Specimen CWO3 with eccentrically arranged openings and Specimen CWO4 diagonally arranged openings were the same. 3D FEM analyses for CES shear walls with openings were conducted to simulate the experimental behavior and to examine the shear transferring mechanism. The analytical results of shear force versus drift angle relationships and stress transitions at steel flange in boundary beam showed good agreements with experimental results until the maximum strength in all specimens. The analytical result showed that the concrete compressive struts were formed through the wall panels of the second story to that of the first story in Specimen CWO4 with diagonal arranged openings, when the boundary column adjacent to the opening in the first story was subjected to compression. The results also showed that the concrete compressive struts were individually formed in the wall panel of each story due to the effect of tension in a boundary beam in Specimen CWO3 with eccentrically arranged openings and in case that the boundary column adjacent to the opening in the first story was subjected to tension in Specimen CWO4. Thus, the formation of concrete compressive struts obtained from the analytical results almost agreed with that assumed in the modified strut model. Therefore, it is considered that the modified strut model is appropriate as an evaluation method of the shear strength of CES shear walls with openings.